Broccoli is a cruciferous vegetable. Broccoli has been around for more than 2,000 years but has only been commercially grown in the United States since the 1920s. Today, more than 90% of the broccoli harvested in the United States comes from California, although it is also grown in other parts of the country. Broccoli is rich in vitamin C, carotenoids (vitamin A-like substances), fiber, calcium and folate. Broccoli is also a source of many substances called phytochemicals, or plant chemicals, that may have anticancer properties. One of the main phytochemicals in broccoli is thought to provide anticancer properties are isothiocyanates (ITCs). The tumor suppressor gene p53 appears to play a key role in keeping cells healthy and preventing them from starting the abnormal growth that is a hallmark of cancer. When mutated, p53 does not offer that protection, and those mutations occur in half of all human cancers. ITCs might work by targeting this gene. They found that ITCs are capable of removing the defective p53 protein but apparently leave the normal one alone
Some research has suggested that sulforaphane, a substance that is present at much higher levels in broccoli sprouts than in the mature vegetable, may be a powerful cancer-preventing agent. Some researchers have suggested that eating small amounts of broccoli sprouts may protect against the risk of cancer as effectively as much larger amounts of the mature vegetables. We are not aware of any clinical studies that have been done in humans to verify this claim.
The anti-cancer effects of any single food cannot be completely understood without looking at it as part of a bigger dietary picture. It is still unclear, for example, whether the phytochemicals in broccoli have benefit on their own or whether it is the vitamin C, beta carotene, folate, and other compounds, working together and in the right quantities, that might protect people against cancer.